Reconfigurable optoelectronic circuit

ABSTRACT

A reconfigurable optoelectronic circuit adapted to alter its internal configuration includes logic circuits, electric connections and optical connections. It comprises a plurality of logic blocks of electronic circuit and an optical circuit interconnecting them and both the internal configuration of each of the logic blocks and the optical interconnections of the logic blocks using the optical circuit are alterable.

TECHNICAL FIELD

This invention relates to a reconfigurable optoelectronic circuit thatcomprises a mixture of electronic circuits and optical circuits and isadapted to change its internal circuit configuration (including logicalfunctions, electric connections, optical connections and so on) with anenhanced level of freedom.

BACKGROUND ART

In recent years, personal computers, mobile phones and PDAs (personaldigital assistants) have been required to selectively operate with aplurality of applications by switching from one to another in additionto be compact and lightweight and show a high processing speed.Meanwhile, control devices of robots are required to selectively operatewith a plurality of control algorithms by switching from one to anotheron a real time basis. From this point of view, there is a strong demandfor circuit boards carrying reconfigurable circuits, particularly thosethat allow the circuits to be reconfigured at high speed on a real timebasis.

Examples of known reconfigurable circuits include FPGAs (fieldprogrammable gate arrays) and CPLDs (complex programmable logicdevices). Multi-chip systems using an FPGA where chips areinterconnected by electric bus wiring are also known (Japanese PatentApplication Laid-Open No. 2000-311156). Additionally, improvements arerequired to known circuits of the type under consideration in terms ofprocessing speed and circuit scale.

However, since a system disclosed in the above patent document isrealized by connecting chips by electric bus wiring, it does not allowreconfiguration of the inter-chip connections with an enhanced degree offreedom.

DISCLOSURE OF THE INVENTION

In view of the above identified circumstances, the present inventionprovides a reconfigurable optoelectronic circuit adapted to alter (i.e.reconfigure) its internal configuration including logic circuits,electric connections and optical connections, comprising a plurality oflogic blocks of electronic circuit and an optical circuitinterconnecting them, wherein both the internal configuration of each ofthe logic blocks and the optical interconnections of the logic blocksusing the optical circuit are alterable.

There can be a number of different modes of carrying out the inventionthat provides the above described basic arrangement.

Preferably, said optical circuit includes a sheet-shaped opticaltransmission medium and ports adapted to at least either transmit anoptical signal to or receive an optical signal from the opticaltransmission medium, the inter-port optical connections being arrangedso as to flexibly allow alterations.

Preferably, closely located ones of the logic blocks can beinterconnected by electric wires.

Preferably, each of said logic blocks includes a plurality of logicelements and an electric connection network interconnecting the logicelements and at least either the internal configuration of at least oneof the logic elements is or the interconnections of the logic elementsare alterable. For example, each of the logic blocks may include logicelements whose functions are alterable and an electric connectionnetwork that can alter the interconnections of the logic elements.

Preferably, configuration data are distributed by way of said opticalcircuit and the internal configuration of any of the logic blocks isaltered according to the configuration data. Alternatively, it may be soarranged that each of said logic blocks comprises a variable logicsection and a memory section, and the memory section holds configurationdata that corresponds to the internal configuration of the variablelogic section. Then, it may be so arranged that said logic blocks canmove, copy and/or replace the internal configuration of some other logicblock by way of the optical circuit.

In another aspect of the invention, there is provided a hierarchicallyreconfigurable circuit, comprising a first stratum having a plurality oflogic elements whose internal configurations are alterable, a secondstratum containing logic blocks having electric wires and switchesarranged in the form of a matrix and interconnecting the arranged logicelements and adapted to switch the interconnections of the logicelements and a third stratum having a sheet-shaped optical transmissionmedium for optically interconnecting the logic blocks and adapted toswitch the interconnections of the logic blocks.

In still another aspect of the invention, there is provided aninterconnection structure, comprising electric wires interconnectinglogic elements, electric switches adapted to alter the interconnectionsof the logic elements, ports connected to the logic elements and adaptedto perform opto-electric signal conversions and a means for alteringoptical interconnections of the ports by way of a sheet-shaped opticaltransmission medium.

A key feature of the present invention resides in that reconfigurableelectronic circuits (realized typically by semiconductor chips) arehybridized with an (reconfigurable) optical circuit. The presentinvention provides a number of effects and advantages including at firstthat the problem of RC signal delay of electric wires and EMI ofelectronic circuits can be alleviated by applying an optical circuit(typically a flexible optical circuit described latter) withreconfigurable electronic circuits and hence it is possible to realize alarge and complicated circuit that can be reconfigured at high speed.

More specifically, reconfigurable electronic circuits including FPGAsrequire the use of a large number of wires in order to enhance thefreedom of wiring so that consequently a large portion of the die areaneeds to be assigned to programmable wires. Additionally, wires arearranged in the form of a matrix in many cases. Then, a large number ofswitches need to be provided along the wires to by turn give rise to aproblem of wire delays. Furthermore, these tendencies become remarkableparticularly when a large scale and high speed operation is required.

According to the present invention, the size and the area of eachelectronic circuit (chip) are not required to be raised (and rather canbe reduced) as an optical circuit is introduced among the electroniccircuits. Additionally, a substantially large system can be realized byinterconnecting a plurality of electronic circuit by means of an opticalcircuit that operates at high speed. Furthermore, the interconnectionsamong the electronic circuits can be altered with an enhanced degree offreedom by using a flexible optical circuit so that it is possible toreconfigure a large scale circuit comprising a plurality of electroniccircuits.

Generally, it is difficult to make a large electronic circuit operate athigh speed. However, according to the present invention, it is possibleto realize a large scale circuit that operates at relatively high speedby interconnecting small and fast electronic circuits. The use ofsmall-sized electronic circuits, which are inexpensive as compared tolarge ones, reduces the overall cost. Additionally, the overall circuitdimensions can be scalably increased by increasing the number ofelectronic circuits.

While the above cited Japanese Patent Application Laid-Open No.2000-311156 discloses a technique of electrically connecting FPGAs. Whencompared with the above-identified invention, the present invention canimprove the variety and the flexibility of connection by the use of anoptical circuit and makes high speed information transmissions possible.Particularly, while the degree of freedom of the inter-chip electricalconnection is reduced when the number of electronic circuits (chips)increases, the counterpart of a flexible optical circuit is remarkablyhigh because it is adapted to complete connection and multicasttransmissions, etc.

Additionally, it is difficult to reconfigure large electric systems withconventional inter-chip connections using electric wires typically inthe form of matrix wiring. To the contrary, such reconfigurations can berealized relatively easily when optical free wiring is used.Particularly, wire arrangement and circuit design can be remarkablyfacilitated when an optical interconnection is used for long distanceconnection so that the overall circuit can be reconfigured with ease andthe time necessary for the reconfiguration is reduced.

Thus, a large scale reconfigurable circuit that operates flexibly athigh speed can be realized with ease by using an optoelectronic circuit,a hierarchically reconfigurable circuit and/or an interconnectionstructure according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the principle of connection of areconfigurable optoelectronic circuit according to the invention;

FIG. 2 is a schematic plan view of a reconfigurable optoelectroniccircuit according to the invention, showing the configuration thereof;

FIG. 3 is a schematic cross sectional view of a reconfigurableoptoelectronic circuit according to the invention, showing theconfiguration thereof;

FIG. 4 is a schematic illustration of the reconfiguration of theoptoelectronic circuit used in Example 2;

FIG. 5 is a schematic illustration of the reconfiguration of theoptoelectronic circuit used in Example 3;

FIG. 6 is a schematic illustration of the reconfiguration of theoptoelectronic circuit used in Example 4;

FIG. 7 is a schematic illustration of the reconfiguration of theoptoelectronic circuit used in Example 5;

FIG. 8 is a schematic illustration of the reconfiguration of theoptoelectronic circuit used in Example 6;

FIG. 9 is a schematic illustration of the reconfiguration of theoptoelectronic circuit used in Example 7;

FIG. 10 is a schematic illustration of the reconfiguration of theoptoelectronic circuit used in Example 8;

FIG. 11 is a schematic illustration of the reconfiguration of theoptoelectronic circuit used in Example 9;

FIG. 12 is a schematic plan view of the configuration of theoptoelectronic circuit comprising an ASIC and memory used in Example 10;

FIGS. 13A and 13B are schematic exemplar illustrations of propagation oflight in a two-dimensional optical waveguide; and

FIGS. 14A, 14B and 14C are schematic illustrations of examples ofoptical coupling section of port.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in greater detail byreferring to the accompanying drawings that illustrate preferredembodiments of optoelectronic circuit, hierarchically reconfigurablecircuit and interconnection structure according to the invention.

FIG. 1 is a schematic illustration of the circuit connection of anembodiment of reconfigurable optoelectronic circuit, hierarchicallyreconfigurable circuit and interconnection structure according to theinvention. In FIG. 1, there are shown logic elements 201, electricconnection networks 202, a flexible optical circuit 204, logic blocks205, an optical transmission medium 101 and ports 102. Thus, thisembodiment comprises a plurality of electronic circuits, or logic blocks205, whose internal circuit configuration is reconfigurable and whichare interconnected by a flexible optical circuit 204. Examples ofreconfigurable electronic circuit that can be used for the purpose ofthe present invention typically include circuits comprising logicelements 201 whose logic functions can be altered and electricconnection networks 202 adapted to alter the interconnection of thelogic elements 201. In this letter of specification, a unit ofelectronic circuit whose internal configuration is alterable is referredto as logic block. As may be clear from the above description, a typicaloptoelectronic circuit according to the invention comprises a pluralityof electronic circuits (logic blocks 205) and a flexible optical circuit204 that interconnects them, wherein the internal configuration of eachof the logic blocks is reconfigurable and the optical interconnectionsof the logic blocks can be altered with an enhanced degree of freedom.

The logic elements 201 may be LUTs (lookup tables) storing a truth valuetable for input/output relating to the logic function to be realized inthe form of RAM and adapted to output an output signal for a combinationof inputs. They may additionally comprise one or more than one ANDcircuits, NAND circuits, OR circuits, NOR circuits, XOR circuits, flipflop circuits, latch circuits, registers, inverters, multipliers or someother circuits or combinations of any of them. Further, they maycomprise memories. Furthermore, they may also comprise an operation unit(processor) for integer operations, floating point operations, functionoperations and so on.

The electric connection networks 202 are adapted to selectively definethe interconnection of the logic elements. For example, an electricconnection network 202 may comprise electric wires and switches arrangedin the form of a matrix to interconnect the logic elements that arearranged as shown in FIG. 2. The switches are arranged at connectingsections 207 of logic elements 201 and electric wires and also atintersections 206 of wires 208 of the matrix wiring.

Thus, a typical logic block 205 may be defined as a reconfigurableelectronic circuit in which reconfigurable logic elements 201 areinterconnected by a reconfigurable electric connection network 202. Thelogic blocks 205 may include FPGAs, CPLDs and/or processor arrays formedby two-dimensionally arranging processors.

The flexible optical circuit 204 is a circuit adapted to transmitinformation, using light as carrier. It is a circuit that transmitsinformation by way of an optical transmission medium 101 and can alterthe form of transmission of information with an enhanced degree offreedom. The optical transmission medium may typically be a 2D(two-dimensional) optical waveguide. Due to the use of a flexibleoptical circuit 204, it is possible to alter the interconnection of anydesired logic blocks 205 with an enhanced degree of freedom. Thus, anoptoelectronic circuit according to the invention is adapted to alterthe interconnection of any desired logic elements with an enhanceddegree of freedom by altering the related electric connection network(s)and the optical circuit(s). In other words, the entire circuitconfiguration can be altered by altering not only the internalconfiguration of any of the electronic circuits (logic blocks) but alsothe optical interconnection of the selected electronic circuits (logicblocks) with an enhanced degree of freedom.

An optoelectronic circuit according to the invention may alternativelybe embodied as a hierarchically reconfigurable circuit having threestratums adapted to reconfiguration as described below. The threestratums include a first stratum having reconfigurable logic elements(reconfiguration of logic elements), a second stratum having electricwires and switches arranged in the form of a matrix and interconnectingthe arranged logic elements and adapted to alter the interconnection ofany of the logic elements (reconfiguration at the level of the electricconnection networks within the logic blocks) and a third stratum havingan optical transmission medium in the form of a sheet or the like foroptically interconnecting the logic blocks and adapted to switch any ofthe optical interconnections of the logic blocks (reconfiguration at thelevel of the flexible optical circuit).

Due to the use of such a hierarchical structure, it is possible toflexibly realize circuit alternations over a broad range, includingsmall scale alterations using reconfigurations in the first stratum andlarge scale alterations involving those in the third stratum.

A circuit according to the invention may be understood as aninterconnection structure where logic elements are interconnected bymeans of a connection structure comprising electric wiresinterconnecting logic elements, electric switches that can alter any ofthe interconnections of the logic elements, ports electrically connectedto logic element so as to convert electric signals, a sheet-shapedoptical transmission medium that allows optical interconnections of theports and means for altering any of the optical interconnections of theports.

FIG. 2 is a schematic illustration of the configuration of the abovedescribed embodiment of reconfigurable optoelectronic circuit. Referringto FIG. 2, there are shown logic elements 201, a matrix wiring 208 thatis an electric connection network, logic blocks 205, an opticaltransmission medium 101, wire intersections 206 and connecting sections207. It will be appreciated that FIG. 1 illustrates the interconnectionsof the components of the circuit, whereas FIG. 2 illustrates atwo-dimensional layout of the components of the circuit.

Referring to FIG. 2, the reconfigurable circuit comprises a total ofnine logic blocks 205. Each of the logic blocks 205 comprisestwenty-five logic elements 201 and a matrix wiring 208 interconnectingthe logic elements 201. However, the number of logic blocks 205 and thatof logic elements 201 are not limited to those cited above and anydesired numbers may be selected for the purpose of the invention. Thelogic elements 201 are interconnected by horizontal electric wires andvertical electric wires of the matrix wiring 208. Switches are arrangedrespectively at the intersections 206 of the horizontal electric wiresand the vertical electric wires so as to alter any of theinterconnections of the logic elements 201. Alternatively, switches maybe arranged respectively at the connecting sections 207 of the logicelements 201 and the corresponding electric wires.

Said logic blocks 205 are connected to respective ports 102 (see FIG. 1)that are adapted to transmit optical signals to and/or receive opticalsignals from the optical transmission medium 101 (although the ports arenot shown in FIG. 2). Each of the ports 102 comprises an optical outputsection (light emitting element) adapted to convert an electric signalinto an optical signal and/or an optical input section (light receivingelement) adapted to convert an optical signal into an electric signal,although it preferably comprises both an optical output section and anoptical input section from the viewpoint of functionality. Thus, thesignal from a logic block 205 is converted into an optical signal by thecorresponding port 102 and propagated through the two-dimensionaloptical waveguide that is the optical transmission medium 101. Then, itis converted into an electric signal by a different port 102 toestablish an optical circuit. In other words, light emitted from thelight emitting element, or the optical output section, of a signaltransmitting port 102 is propagated through the optical transmissionmedium 101 and input to the light receiving element, or the opticalinput section, of a signal receiving port 102. As the signal isconverted into an electric signal by the signal receiving port 102, thesignal is transmitted from the former port 102 to the latter port 102 toestablish an optical circuit.

The optical transmission medium 101 is typically a two-dimensionaloptical waveguide (a sheet-shaped optical waveguide). A typical flexibleoptical circuit refers to a two-dimensional optical waveguide thatallows any desired optical devices to be arranged respectively at anydesired positions thereof so that optical data may be two-dimensionallytransmitted from a port arranged at a desired position to another portarranged at another desired position. For example, as shown in FIGS. 13Aand 13B, the destination of signal transmission can be selected in adesired manner by making light 103 to be propagated from a port 102 witha sense of propagation and an angle of radiation of light 104 a or 104 bthat are predefined appropriately. Although the predefinable range ofradiation angle 104 is not limited, it is possible to select 360° forbroadcasting light in all directions or select a small angle so as tomake light to be emitted in the form of a beam from a light emittingelement with a small radiation angle, which may correspond to theradiation angle of the light emitting element. Thus, the entire circuitcan be altered with an enhanced degree of freedom by controlling thesense of propagation of light and the angle of radiation of light. Withregard to one to one connection/combination of ports, the flexibleoptical circuit can combine any ports for bidirectional communications.In other words, it is a circuit adapted to complete connection. It is acircuit with an enhanced degree of freedom for connection that iscapable of realizing 1:N multicast communications and N:Mcommunications.

Additionally, the flexible optical circuit can switch and reconfigurethe above described connections. More specifically, it can switch(reconfigure) a one to one combination of ports and also switch(reconfigure) any of the transmission paths among a plurality of portsincluding 1:N and N:M transmission paths.

In this way, the flexible optical circuit that comprises atwo-dimensional optical waveguide is adapted to complete connection ofports and reconfiguration for multicast communications and has anenhanced degree of freedom for connectivity. Thus, it is a preferablereconfigurable system that interconnects reconfigurable electroniccircuits by a reconfigurable optical circuit with an enhanced degree offreedom for interconnection.

Then, it is possible to smoothly reconfigure an optoelectronic circuitover a plurality of electronic circuits (chips) interconnected by way ofa flexible optical circuit. Therefore, it is possible to reduce longdistance electrical wirings in logic blocks and alleviate the problem ofsignal delays within electronic circuits. Furthermore, it realizes alarge and fast system using small electronic circuits (chips).Additionally, it is possible for an optical circuit comprising atwo-dimensional optical waveguide to expand system size in a scalablemanner by adding logic blocks.

Moreover, the use of a reconfigurable optical circuit with atwo-dimensionally enhanced degree of freedom for interconnection asdescribed above is highly preferable from the viewpoint of easiness ofdesigning particularly when expanding electronic circuits (logicblocks), each comprising two-dimensionally arranged logic elements. Inother words, the hybridization of a two-dimensional flexible opticalcircuit and electronic circuits is very advantageous particularly interms of applicability and adaptability.

While square logic blocks 205 are arranged regularly in FIG. 2, theprofile of the electronic circuits that can be used for the purpose ofthe present invention is by no means limited thereto. The electroniccircuits may have a rectangular profile and may be arranged in anydifferent way. Particularly, ports may be arranged at any desiredpositions of a two-dimensional flexible optical circuit. In other words,an optoelectronic circuit comprising a two-dimensional flexible opticalcircuit is characterized by providing an advantage of an enhanced degreeof freedom for arranging chips (electronic circuits).

Typically, each logic block may be connected with a port, although eachlogic block may alternatively be provided with a plurality of ports.Still alternatively, a plurality of logic blocks may share a singleport.

While FIG. 2 shows a homogeneous reconfigurable system comprising onlylogic blocks 205, a reconfigurable optoelectronic circuit according tothe invention may additionally comprises chips, which may be one or morethan one ASICs, CPUs, DSPs and/or memories. Then, ports connected tochips such as ASICs may be provided.

Not a line waveguide or free space optical connection but atwo-dimensional optical waveguide is preferably used for a flexibleoptical circuit according to the invention as will be discussed below.Firstly, the use of an optical circuit using optical fibers and/or aline waveguide may be conceivable. Then, however, fixed line wiring isrequired for such an arrangement at the cost of freedom of wiring.Additionally, there may be difficulties including provision of a largenumber of optical switches when such an optical circuit is to bereconfigured. Furthermore, a linear optical waveguide has a dimension ofseveral microns to tens of several microns and alignment of the opticalaxis of such an optical waveguide is highly difficult. Stilladditionally, micro-processing are required to fabricate such an opticalwaveguide.

On the other hand, the use of a two-dimensional optical waveguide allowsoptical devices (including light emitting elements and light receivingelements) to be mounted at desired positions. In other words, it ispossible to transmit information between any desired positions.Additionally, optical devices and an optical waveguide layer can beoptically aligned with ease when optically coupling them. Because ofsuch simplicity of arrangement, a circuit board can be prepared withease to reduce the cost. Still additionally, as will be discussedhereinafter, with a flexible optical circuit comprising atwo-dimensional optical waveguide, optical circuits can be reconfiguredbasically only by controlling the ports thereof that are opticalinput/output sections.

While a system adapted to allow light to be propagated in a free spaceis accompanied by a problem of large dimensions, although it provides anenhanced degree of interconnection freedom, the use of a flexibleoptical circuit comprising a two-dimensional optical waveguide allows torealize a circuit board on which circuits can be mounted to show a lowprofile and high density.

Now, a method of altering the circuit configuration of a reconfigurableoptoelectronic circuit according to the invention will be describedbelow. As pointed out above, the circuit can be reconfigured in any ofthe three stratums.

The three stratums refer to the level of the logic elements, that of theelectric connection networks within the logic blocks and that of theflexible optical circuit. Basically, an optoelectronic circuit accordingto the invention can be reconfigured repeatedly without any limit. Thecircuit can be reconfigured entirely or partly. Data to be used forreconfiguration are referred to as configuration data (configurabledata). The circuit configuration is altered according to theconfiguration data. The configuration data are stored in the inside ofthe optoelectronic circuit or in an external memory device and anoperation of reconfiguration is conducted by reading out theconfiguration data whenever necessary. Either electric wires or theflexible optical circuit may be used for loading the configuration data,although the use of the flexible optical circuit is advantageous fromthe viewpoint of exploiting the features of an optoelectronic circuitaccording to the invention.

A reconfiguration at the first stratum, or the level of the logicelements, is realized by altering the internal configuration of any ofthe logic elements to select and/or alter the function of the relatedlogic element(s). A logic element can be electrically redefined so as tobe provided with one of a plurality of logic functions. For example, anLUT can be redefined or rewritten into a logic circuit having a truthvalue table of a specific logic function by inputting a specific signalto the LUT. For example, an LUT can realize wide range logic functionswith about 2 to 6 inputs.

When an ALU (arithmetic and logic unit) is used as logic element, itsfunction can be defined by means of an instruction set to be input. ALUsof a plurality of different types may be provided so that a desired ALUmay be selectively used. For example, ALUs of the integer type, those ofthe floating point type and those with different numbers of bits may bearranged. A reconfiguration technique using part of the configurationdata as control signals for a multiplexer or a selector may also be usedfor the purpose of the invention.

All the logic elements may be reconfigured. Alternatively, only some ofthe logic elements may be reconfigured. If the net result is same, thelatter partial reconfiguration is preferable because the reconfiguringoperation can be carried out more quickly when only part of the logicelements are involved in reconfiguration. A memory such as SRAM may beprovided inside or near each logic element so as to store configurationdata there. It will be appreciated that an optoelectronic circuitadapted to reconfiguration of only the second and third stratums andhence not adapted to reconfiguration of the first stratum (all or partof the logic elements) also falls within the scope of the presentinvention.

The second stratum at the level of the electric connection networks isreconfigured by switching all or some of the switches arranged at thesections connecting the logic elements and the matrix wiring and also atthe intersections of wires of the matrix wiring to redefine the routingof the electric connection network(s) (see FIG. 2). The interconnectionsof the logic elements can be altered and redefined by turning theswitches on/off, using part of the configuration data. The switches atthe intersections can be turned on/off typically by controlling thegates of the pass transistors. In this way, a logic element is connectedto another logic element by way of a horizontal electric wire, avertical electric wire and a switch. A horizontal electric wire and avertical electric wire can be connected to each other by way of a logicelement.

In this way, the logic function of each logic element and theinterconnection of any two logic elements can be reconfigured accordingto the configuration data. Then, a logic block can be reconfigured byrewriting the configuration data in the logic block. For the purpose ofthe present invention, a logic block can typically be defined as anelectronic circuit whose internal configuration can be reconfigured byaltering the logic function of each of the logic elements and theinterconnections of the logic elements. Each logic block may be providedwith a memory such as SRAM for storing the configuration data in theinside. Memories that can be used for the purpose of the inventioninclude flash memories, EEPROMs, DRAMs, SRAMs, MRAMs and Fe-RAMs.

The function of a reconfigurable circuit according to the invention isdefined by specifying the interconnections of the logic blocks asdescribed below in addition to the logic function of each of the logicelements and the interconnections of the logic elements.

The third stratum at the level of the flexible optical circuit can bereconfigured by controlling the optical outputs from the port connectedto a logic block and/or classifying the optical inputs to the ports. Theinterconnections of the logic blocks can be defined and altered bycontrolling the connections of the flexible optical circuit, using partof the configuration data for specifying the definition and thealteration.

As pointed out above, the circuit connections can be altered(reconfigured) by altering the sense of propagation and the angle ofradiation of the light signal from the signal transmitting port toselect the destination of the signal. It is also possible to alter thedirection in which the optical signal is received. It is also possibleto reconfigure the circuit by selecting data at the signal receivingport. For example, it is possible to transmit information to a desiredsignal receiving port by an arrangement where the signal transmittingport transmits the information by broadcast as packet signals to whichaddresses are attached and the signal receiving port selects the rightaddress. Thus, a flexible optical circuit is a circuit that canintrinsically realize bidirectional complete coupling of ports.

While logic blocks can be optically interconnected, specific logicblocks such as those that are located close to each other mayalternatively be interconnected directly by electric wiring. However, itshould be noted that logic blocks that are remote from each other arepreferably interconnected by optical wiring. It may be so arranged thatoptical wiring and electric wiring can freely and selectively be used.

Due to the provision of the third stratum, logic blocks can be connectedto other logic blocks by way of the flexible optical circuit with anenhanced degree of interconnection freedom. Thus, as a result, it ispossible to realize a large reconfigurable circuit that can bereconfigured over a plurality of logic blocks.

By applying the hierarchical structure of the first, second and thirdstratums, logic elements and logic blocks can be interconnected in ahighly flexible way according to configuration data.

One or more than one stratums may be added to the above three stratums.For example, a stratum of electric connection networks of a differentform may be arranged between the second and third stratums. Then,corresponding relationship between the logic blocks and the ports can bealtered by reconfiguring the electric connection networks. Networks ofoptical fiber may be provided as fourth stratum. The advantages ofproviding the above three stratums can be fully exploited when a fourthstratum is added.

An additional control circuit may be provided for the purpose ofinputting/outputting and/or transferring configuration data and/orissuing commands for reconfiguration. The control circuit may beassigned to some of the logic blocks. The use of the flexible opticalcircuit for transferring configuration data to logic blocks ispreferable because it allows a quick reconfiguration. Then, areconfiguration can be realized dynamically on a real time basis. Thecircuit can be reconfigured optimally to make it currently most suitablefor the processing operation to be performed at high speed by frequentlyreconfiguring logic blocks.

FIG. 3 is a schematic cross sectional view of an embodiment ofoptoelectronic circuit according to the invention. In FIG. 3, there areshown electric wiring layers 105, electric wires 106 and electronicdevices (chips) 107 that are logic blocks. As shown in FIG. 3,reconfigurable electronic devices 107 and an optical circuit comprisinga two-dimensional waveguide as optical transmission medium 101 coexistsin the circuit board. Additionally, the electric wiring layers 105comprising electric wires 106 that interconnect the chips 107 are laidto realize a compact assembly. The flexible optical circuit is soconfigured that a signal from one of the electronic devices 107 isconverted into an optical signal at the corresponding port 102 and,after being propagated through the optical transmission medium 101, theoptical signal is converted into an electric signal by some other port102.

While FIG. 3 is a schematic cross sectional view of a circuit comprisingthree chips 107 a through 107 c and three ports 102 a through 102 c, anynumber of logic blocks (chips) and any number of ports may be arrangedon a same plane as shown in the plan view of FIG. 2. While the ports 102are arranged on the optical transmission medium 101 in direct contactwith the latter, the arrangement of the ports 102 is by no means limitedthereto. Alternatively, the ports may be buried in the opticaltransmission medium 101 so as to directly couple light to the waveguideor arranged on an end facet of the optical transmission medium 101.

The optical transmission medium 101 may be made of any appropriatematerial selected from glass, semiconductor or an organic material solong as it transmits propagating light 103 with a sufficiently hightransmittance. For example, a commercially available glass substrate, asingle crystal substrate of lithium niobate, a semiconductor substrateof Si or GaAs or an organic sheet of polycarbonate, acryl, polyimide orpolyethylene terephthalate may be used without any further treatment.Techniques that can be used for preparing the optical transmissionmedium 101 include vacuum evaporation, dipping and application as wellas molding such as injection molding and extrusion molding. A clad layermay be formed by coating the substrate with a layer showing a differentrefractive index. The size of the optical transmission medium 101 istypically between about 100 microns and tens of several centimeters inview of the fact that information is transmitted betweentwo-dimensionally arranged desired positions, although it may depend onthe data transfer rate. The thickness of the optical transmission medium101 is typically between 1 micron and several centimeters, although itis preferably between 50 microns and several millimeters from theviewpoint of easiness of alignment of the optical axis of the opticalwaveguide.

The optical output section of each port 102 is adapted to propagatelight 103 on the plane of the two-dimensional optical waveguide with anappropriate radiation angle. On the other hand, it can propagate in amultiple mode or single mode, although either mode may be used for thepurpose of the invention.

While light emitting elements that can be used for the optical outputsection of a port 102 include laser diodes and LEDs, the use of asurface emitting laser having a small angle of light emission ispreferable from the viewpoint of realizing propagation of light with asmall radiation angle. The optical output section of a port 102 may beprovided with a means for switching the radiation angle and thedirection of emission. With such an arrangement, the two-dimensionaloptical waveguide 101 can make the ports 102 emit light so as topropagate it in different directions with different radiation angles ina switched manner. As means for switching the radiation angle and thedirection of emission, each port 102 may be provided with a plurality ofoptical output sections so as to be able to emit light in differentdirections with different radiation angles and a specific direction ofemission of light and a specific radiation angle may be selected byelectrically selecting an optical output section to be used for signaltransmission. For example, a plurality of light emitting elements may bearranged in array and different radiation angles and differentdirections of light emission may be discerned and defined for each ofthe elements of the array so that one of the directions and one of theradiation angles may selectively be used. Then, the radiation angle andthe direction of light emission can be discerned and defined byselecting one of the light emitting elements of the array.

Furthermore, devices that are adapted to control the radiation angle andthe direction of light emission can be used as light emitting elementsfor the optical output sections of the ports. The radiation angle andthe direction of light emission can be altered by making the mode ofcoupling the light emitting elements that are used for the opticaloutput sections and the two-dimensional optical waveguide 101 variable.More specifically, such an alteration can be realized by moving theoptical coupling section arranged in the vicinity of the light emittingelement in question, which may be a mirror, a prism, a lens or agrating. A similar effect can be obtained by moving the light emittingelement itself or by modulating the optical properties including therefractive index of the material of the optical coupling section. Amovable optical coupling section can be realized by forming a movablemicro-mirror, employing an electrostatic force element, a magnetic forceelement or a piezoelectric element and the micro-mechanics technology.

On the other hand, the optical input section of a port 102 is preferablyadapted to receive light over all directions of 360° of thetwo-dimensional optical waveguide 101. This arrangement provides anadvantage that all the optical input sections can be made to have a sameand simple configuration. Of course, each of the optical input sectionsmay be so arranged that it can receive light only in a predetermineddirection relative to the two-dimensional optical waveguide. Lightreceiving elements that can be used for the optical input sectionsinclude PIN photodiodes and MSM photodiodes. An optical coupler can alsobe applied to the optical input section. From the above described pointof view, the use of a conical or spherical mirror is preferable for theoptical coupler to be applied to the optical input section because lightis preferably received in any direction over intra-planar 360 degrees.

A plurality of light receiving sections arranged in array may be usedfor a port 102. Particularly, the light receiving sections may bearranged in such a way that the elements of the array are adapted toreceive incident light in different respective directions. Then, thedirection in which light strikes the port 102 can be discerned byselecting a light receiving section out of the array.

The optical transmission medium 101 can be arranged on any appropriatesubstrate 100. A printed substrate, a metal substrate of aluminum orSUS, a semiconductor substrate of Si or GaAs, an insulating substrate ofglass or some other material, a resin-made substrate or sheet of PMMA,polyimide or polycarbonate may be used for the substrate 100.

The electric wires 106 are metal wires of aluminum or copper. They canbe prepared by vacuum evaporation or by using a technique of formingthem from electrically conductive paste by screen printing.Alternatively, a technique of laying metal foils such as electrolyticcopper foils to form a multilayer and chemically etching the metalfoils, using etching resist in the form of a desired pattern, to producea circuit conductor pattern may be used. While the optoelectroniccircuit of FIG. 3 has only a single layer of optical transmission medium101, it may alternatively have a plurality of layers of opticaltransmission medium 101.

As described above by way of embodiments, an optoelectronic circuitboard according to the invention is adapted to alter the configurationof the electronic devices (logic blocks) and that of the opticalcircuits. In other words, an optoelectronic circuit according to theinvention can be reconfigured in a highly reliable and flexible way.Additionally, a circuit substrate having an optical transmission mediumas described above provides an enhanced degree of design freedom and ishighly adapted to reconfiguration. Also, such a circuit substrate canhandle a large volume of information at high speed and is highlyresistive against electromagnetic radiation noises.

Now, the present invention will be described further by way of specificexamples. However, it should be noted that the present invention is byno means limited to the examples that are described below particularlyin terms of configuration and manufacturing process and any variationsthereof that are found within the above described concept are alsowithin the scope of the present invention.

EXAMPLE 1

An optoelectronic circuit or a circuit board similar to thoseillustrated in FIGS. 2 and 3 is prepared in Example 1. As shown in FIG.3, the reconfigurable optoelectronic circuit of this example comprisesan optical transmission medium 101 of a two-dimensional opticalwaveguide, ports 102, electric wiring layers 105 containing electricwires 106 and semiconductor chips 107 having reconfigurable electroniccircuits. To be more accurate, the optical transmission medium 101 issandwiched between a pair of electric wiring layers 105 a, 105 b in thisexample. The ports 102 are arranged near the interface of the electricwiring layer 105 a and the optical transmission medium 101. The size ofthe substrate 100 is 3 cm square. A total of nine semiconductor chips107 ([1, 1] through [3, 3]) that correspond to the logic blocks 205shown in the plan view of FIG. 2 are arranged. Each of the semiconductorchips 107 is connected to a port 102.

The optical transmission medium 101 is formed by a two-dimensionaloptical waveguide that is produced by coating a 100 μm thick piece ofpolycarbonate (refractive index: 1.59) with clad layers of fluorinatedpolyimide (refractive index: about 1.52). The optical transmissionmedium 101 is bonded to the electric wiring layers 105 that is mountedwith electric devices 107 to produce a highly densely mountedoptoelectronic multilayer substrate as shown in FIG. 3.

The electric signal (CMOS logic or the like) of each semiconductor chip107 can be transmitted by way of the corresponding port 102 and theoptical transmission medium 101 as optical signal. It is also possibleto transmit an electric signal to a nearby semiconductor chip 107 by wayof the related electric wire 106. Either transmission of an opticalsignal or that of an electric signal can be selected depending on thecircumstances. The logic signal (e.g., 3.3V in the case of a CMOS) ofthe semiconductor chip 107 is a voltage that is sufficiently high fordriving the light emitting element of the port 102. The electric signalis converted into an optical signal as a forwardly biasing logic signalto the light emitting element of the port 102 by applying the logicsignal. A 0.85 μm band surface emission laser VCSEL) is used for thelight emitting element. The characteristics of the individual VCSELsinclude a drive current of 3.0 mA and an optical output level of 3 mW.Light emitted from the light emitting element is propagated through theoptical transmission medium 101 with a predetermined radiation angle.

The ports 102 of this example are formed so as to provide differentradiation angles and different directions of light emission forpropagation. For this purpose, mirrors having a profile of aquadrangular pyramid as shown in FIG. 14A are used as optical couplers301. Light 303 from one of the light emitting elements 306 is irradiatedto the pyramidal mirror 301 from above and reflected transversallybefore it is coupled to the optical transmission medium 101. When light303 is irradiated onto one of the slanting surfaces of the pyramidalmirror 301 (position 302 of light irradiation) from one of the lightemitting elements as shown in FIG. 14B, light 304 propagating with aradiation angle of about 90° is produced. When, on the other hand, lightis irradiated on the four slanting surfaces of the pyramidal mirror 301(position 302 of light irradiation) as shown in FIG. 14C, light 304propagating with a radiation angle of 360° is produced. When light 303is irradiated onto two or three slanting slopes of the pyramidal mirror301, a radiation angle of 180° or 270°, whichever appropriate, isproduced. Uniform light is propagated through the entire range of theradiation angle because the slanting surfaces are diffusing surfaces.

A light output section 305 is formed by arranging a total of five lightemitting elements 306 a, 306 b, 306 c, 306 d and 306 x, the former fourcorresponding to the four slanting surfaces and the remaining onecorresponding to the center of the pyramidal mirror, above the pyramidalmirror 301 so that light from each of the devices strikes thecorresponding slanting surface. With this arrangement, the radiationangle can be defined by selecting one or more than one of the lightemitting elements. Light is propagated in all directions of 360° whenthe light emitting element 306 x at the center is used and in thedirection of predefined 90° when one of the light emitting elements 306a through 306 d is selected, whereas light is propagated in thedirections of predefined 180° when two of the light emitting elementsare selected and in the directions of predefined when three of the lightemitting elements are selected. Finally, light is propagated in alldirections of 360° when all the four light emitting elements 306 athrough 306 d are selected.

In this example, the radiation angle and the direction of light emissioncan be switched by arranging a plurality of light emitting elements inthe port 102 and selecting the light emitting element(s) to be driven.Then, the flexible optical circuit is reconfigured according toconfiguration data.

The optical signal propagated through the optical transmission medium101 is then taken up by the light receiving element of the target port102 and converted into an electric signal. An Si-PIN photodiode is usedfor the light receiving element and connected to the related electroniccircuit 107. The electric signal obtained by the conversion is takeninto the inside of the LSI located in the vicinity as input electricsignal and then processed. The original CMOS-compatible voltage can berestored when a preamp is integrally arranged with the light receivingelement for the purpose of amplifying the electric signal. The lightreceiving section can receive light in all directions of 360° of thetwo-dimensional optical waveguide 101 when a conical optical couplingsection is used. In this way, the ports 102 can be freely connected byway of the optical transmission medium 101 and the data transfer ratebetween the ports 102 is maximally 1 Gbps and typically 500 Mbps.

Each of the semiconductor chips 107, or the logic blocks, compriseslogic elements, each having a 4-input LUT and a flip flop, arranged inthe form of a matrix. The number of logic elements in each logic blockis about 50 thousands (although only 5×5 logic elements are shown inFIG. 2 for the purpose of simplicity). The electronic circuit 107 can bereconfigured by switching the logic function of the LUTs, the switchesat the connecting sections of the logic elements and the wires and alsothe switches at the intersections of wires of the matrix wiring. Thesize of the chip 107 is 0.6 cm square and the operation frequency is 200MHz.

When the optoelectronic circuit of this example is driven to operate, anoptical circuit is formed between the selected two ports 102 and it wasconfirmed that the circuit operates in the desired manner. Theelectronic circuits 107 in the semiconductor chips can be reconfiguredand the connections of the flexible optical circuit can be altered(reconfigured) by externally reading configuration data. In other words,it is confirmed that the optical circuit comprising means for switchingthe radiation angle and the direction of light emission can bereconfigured according to configuration data with an enhanced degree offreedom. Any desired ports 102 can be connected to each other in theflexible optical circuit and it is possible to realize a desiredmulticast transmission. Thus, a large scale and high-speed operatingcircuit can be reconfigured with an enhanced degree of freedom byreconfiguring the optical circuit and also electrically reconfiguringthe semiconductor chips in a combined manner.

EXAMPLE 2

A reconfigurable circuit is formed in Example 2 by using a circuit boardsimilar to that of Example 1. FIG. 4 is a schematic illustration of anexemplar circuit reconfiguration of the optoelectronic circuit of thisexample. A semiconductor chip having a reconfigurable electronic circuitin Example 1 corresponds to a logic block 205 in FIG. 4.

In FIG. 4, arrows with a dotted line indicate connections using theflexible optical circuit and those with a solid line indicateconnections using electric wires. In this example, the flexible opticalcircuit is used for transferring data between logic blocks 205. Asdescribed below, the flow of data can be altered with an enhanced degreeof freedom by altering the connections of the flexible optical circuit.Each of the logic blocks 205 is provided with a port adapted to transmitand receive light.

The circuit of this example is adapted to alter its internal structure,or reconfigure itself, as it transits from State A to State B in FIG. 4.In FIG. 4, the logic blocks 205 carry various patterns, which indicatethat the circuits differ in terms of circuit configuration. Thus, thedifferent pattern means that the different circuit is developed in thelogic block. In this example, the circuit configuration of each of thelogic blocks 205 is defined by externally loading configurationinformation in advance. In State A, a signal is externally input to thelogic block [2, 1] and processed within the block. Thereafter, the datais transferred to the logic block [3, 3] by the flexible optical circuitand processed in the logic block before it is output. In State B, on theother hand, a signal is externally input to the logic block [2, 1] andoutput from the logic block [3, 3] as in the case of State A, althoughthe signal passes through the logic blocks [1, 3] and [2, 3] in between.The signal is conveyed from the logic block [2, 1] to the logic block[1, 3] by way of the flexible optical circuit and from the logic block[1, 3] to the logic block [2, 3] and then to the logic block [3, 3] byway of electric wires.

A transition of state as described above is realized as configurationdata (information on alterations of connections through the flexibleoptical circuit) is externally written into the memories annexed to theports. Then, the ports alters the mode of transmission/reception of anoptical signal according to the configuration information. In thisexample, a circuit is defined by using two logic blocks 205 in State A,whereas the functions of the logic blocks [1, 3] and [2, 3] are linearlyadded to the data flow in State B. In other words, the function of thecircuit is expanded as a result of reconfiguration of the flexibleoptical circuit.

While only two states are involved in the above description, the numberof states is not limited to two and the circuit can be reconfigured toany one of a number of states. For example, when two logic blocks areinvolved as in State A, a combination of any two logic blocks may beused for reconfiguration. Particularly, data can be opticallytransferred at high speed between logic blocks 205 that are separatedfrom each other by a long distance. In a manner as described above, theoptoelectronic circuit can change its function and one or more than onefunctions may be added to it by reconfiguring the data flow on a blockby block basis. While nine logic blocks are shown in FIG. 4, theadvantages of a flexible optical circuit can be boosted when the numberof logic blocks is raised.

The internal configuration of each of the logic blocks 205 is predefinedand fixed and only the third stratum that is the flexible opticalcircuit is reconfigured in this example. Such a reconfiguration can berealized relatively at high speed because the volume of necessaryconfiguration data is small. While the internal configuration of each ofthe logic blocks 205 is fixed in the above description, the internalconfiguration can be externally rewritten if necessary for the purposeof version up of the system. In such an occasion, this example providesan advantage of raising the degree of freedom for designing a newprogram because the flexible optical circuit has a high degree offreedom of connections.

EXAMPLE 3

Example 3 is similar to Example 2 but the circuit is reconfigured byadding functions in parallel. FIG. 5 is a schematic illustration of anexemplar circuit reconfiguration of the optoelectronic circuit of thisexample. Each of the logic blocks is provided with a port adapted totransmit and receive light. It will be seen that long distancetransmission and multicast using a flexible optical circuit arefunctioning.

Referring to FIG. 5, in State A, a signal is externally input to thelogic block [2, 1] and processed within the block. Thereafter, the datais transferred to the logic block [3, 3] by the flexible optical circuitand processed in the logic block before it is output. In State B, on theother hand, a signal is externally input to the logic block [2, 1] andprocessed. Subsequently, the signal route is branched to path A gettingto the logic block [1, 3], path B getting to logic block [2, 3] by wayof logic block [2, 2] and path C getting to logic block [3, 3]. Theflexible optical circuit is used for the transfer from the logic block[2, 1] to the logic block [1, 3], the transfer from the logic block [2,1] to the logic block [3, 3] and the transfer from logic block [2, 1] tologic block [2, 2] and an electric wire is used for the transfer fromthe logic block [2, 2] to the logic block [2, 3].

A transition of state as described above is realized in this example byaltering the interconnections of the related logic blocks 205 accordingto the control information such as addresses typically described in theheader of the input signal. For example, the use of the flexible opticalcircuit or that of electric wires may be selected. Also, the radiationangle and the direction of radiation may be altered at the transmittingport. In this example, the logic block [2, 1] decodes the signal inputto it and then selects propagation of a beam to the logic block [3, 3](State A) or multicast toward the logic blocks [1, 3], [2, 2] and [3, 3](State B). In other words, in this example, the flexible optical circuitis reconfigured by using the control information such as addressesdescribed in the signal as configuration data. While the transmittingport makes the above described alterations in the above description, theoptical signal may be diffused and propagated so that the receiving portcan decide to acquire the transmitted data or not, according to whetherit is State A or B.

Thus, in this example, while the path C is used in State A, the path Aand the path B are added in parallel for the data flow in State B. Inother words, functions are added as a result of reconfiguration of theflexible optical circuit. Again, the number of states is not limited totwo. Thus, as in the case of Example 2, the optoelectronic circuit canchange its function and one or more than one functions may be added toit by reconfiguring the data flow on a block by block basis.Particularly, multicast transmission, using the flexible optical circuitis effective when the application is provided with the feature ofparallelism.

EXAMPLE 4

Example 4 is similar to Example 3 but involves more complexreconfigurations. FIG. 6 is a schematic illustration of an exemplarcircuit reconfiguration of the optoelectronic circuit of this example.Each of the logic blocks is connected to a port adapted to transmit andreceive light. It will be seen that long distance transmission andmulticast using a flexible optical circuit are functioning.

Referring to FIG. 6, in State A, a signal is externally input to thelogic block [2, 1] and output by way of the logic blocks [1, 3], [2, 3],[3, 1], [3, 2] and [3, 3]. On the other hand, in State B, a signal isexternally input to the logic block [2, 1], while another signal isinput to the logic block [3, 1]. The signal input to the logic block [2,1] proceeds to the logic block [2, 2] by way of the logic block [1, 2].The signal input to the logic block [3, 1] is multicast to the logicblocks [1, 3], [2, 2] and [3, 2]. While the signal to the logic block[1, 3] is output directly, the signal to the logic block [3, 2] proceedsto the logic block [3, 3], where it is output. On the other hand, in thelogic block [2, 2] where the two signals arrive, an arithmeticprocessing operation is conducted by using the signals (e.g., acomparing operation) and the processed signals proceed to the logicblock [2, 3], where they are output.

A transition of state as described above is realized in this example asconfiguration data is externally written into the memories annexed tothe ports and to the logic blocks 205. As a result, each of the logicblocks decides to use electric wires or the flexible optical circuit foroutput and selects the direction and the angle of radiation of theoptical output.

In this example, the serial circuit in State A is reconfigured to aparallel circuit in State B. Particularly, multicast transmission fromthe logic block [3, 1], using the flexible optical circuit makes asophisticated reconfiguration feasible in this example. Moreover, inState B, arithmetic operations between branched data flows are madepossible in the logic block [2, 2] in addition to parallelism. Thenumber of states is not limited to two. Thus, in Example 4 again, theoptoelectronic circuit can change its function and one or more than onefunctions may be added to it by reconfiguring the data flow on a blockby block basis. Particularly, this circuit is a reconfigurable circuitthat is highly advantageous in terms of parallelism.

EXAMPLE 5

In Example 5, the configuration data in a logic block is distributed(multi-casted) by way of the flexible optical circuit. With thisarrangement, the electronic circuit in each of the logic blocks can bealtered with an enhanced degree of freedom according to theconfiguration data that are distributed by light. FIG. 7 is a schematicillustration of an exemplar circuit reconfiguration of theoptoelectronic circuit of this example.

In the optoelectronic circuit of this example, the logic blocks comprisea memory block 209 in addition to the chips, and the memory block 209supplies configuration data that corresponds to the internalconfiguration of each of the logic blocks 205. The memory block 209 maybe a non-volatile memory and appropriate ones of the configuration datastored there may be selectively used. The data stored in the volatilememory may be rewritten from time to time, while the system is beingoperated. The memory may be a flash memory, an EEPROM, a DRAM, an SRAM,an MRAM, an Fe-RAM or some other appropriate memory.

In this example, each of the logic blocks 205 is provided with a portdedicated to signal reception. A port connected to the memory block 209is dedicated to signal transmission. As configuration data are loadedappropriately from the memory block 209 to a desired logic block 205,the electronic circuit in the latter is reconfigured. In FIG. 7, thechange of graphical patterns of the logic blocks 205 indicates that theinternal electronic circuits thereof are reconfigured. In both State Aand State B, a signal is externally input to the logic block [2, 1] andoutput by way of the logic blocks [2, 2], [3, 2], [3, 3], [2, 3] and [1,3]. In other words, the data flow among the logic blocks 205 does notchange in response to a transition from State A to State B or vice versain this example. Electric wires are used for the flow of data in thisexample, although the flexible optical circuit may be used as part ofthe flow of data.

Broadcast transmission is used for the purpose of transmission ofconfiguration data so that the configuration data transmitted from thememory block 209 may be received at all the ports as optical signals.Since the data are transmitted in the form of packets and provided withaddresses that corresponds to the logic blocks 205 so that the portsthat correspond to the addresses can receive the configuration data.

It is not necessary to reconfigure all the logic blocks 205. In FIG. 7,only the logic blocks [2, 1], [3, 2] and [2, 3] are reconfigured. Thedotted lines in FIG. 7 indicate the flows of configuration data. Sincethe flexible optical circuit can transmit information to the desiredlogic blocks 205 by changing the address of the packets, the arrangementof this example functions effectively for such a partialreconfiguration.

Thus, under the constant data flow, the optoelectronic circuit can bereconfigured by way of transmission/reception of configuration data,using the flexible optical circuit. Particularly, since the flexibleoptical circuit is adapted to broadcast and multicast, the arrangementof this example is useful when rewriting the configuration data of aplurality of logic blocks 205 and also when the configuration data needto be partly rewritten. Configuration data can be optically transmittedat high speed to logic blocks 205 that are separated by a long distanceif the number of logic blocks is large.

The optoelectronic circuit of this example is adapted to distributeconfiguration data by using the third stratum and reconfigure theinternal configuration of at least either the first stratum or thesecond stratum. Thus, the arrangement of this example can be used totransmit either the configuration data of the first stratum or those ofthe second stratum by way of the third stratum.

EXAMPLE 6

As in the case of Example 5, the flexible optical circuit of thisexample is used to distribute the configuration data of any of the logicblocks 205. In this example, the data flow among the logic blocks 205 isalso reconfigured. As in the case of Example 5, the configuration of theelectronic circuit in each of the logic blocks 205 can be reconfiguredaccording to the configuration data from the memory block 209. In thisexample again, each of the logic blocks 205 is connected to a portadapted to transmission/reception. As seen from FIG. 8, the flexibleoptical circuit is applied to interconnections of the logic blocks 205and the data flow among the logic blocks 205 is also reconfigured.

Referring to FIG. 8, State A involves a single input and a single outputso that the signal input to the logic block [2, 1] is output from thelogic block [1, 3] by way of six logic blocks (path A). On the otherhand, State B involves two inputs and two outputs so that the signalinput to the logic block [2, 1] is output from the logic block [1, 3] byway of four logic blocks (path A′). Apart from this, there is formed apath B for a signal input to the logic block [3, 1] and output from thelogic block [3, 3]. In other words, in this example, a new function(path B) is inserted into the optoelectronic circuit depending ontransition of state and the original function is diminished from thepath A to the path A′.

In this example again, configuration data is distributed from the memoryblock 209 by using the flexible optical circuit. Note, however, electricwires may be used partly for moving configuration data. The connectionin any of the logic blocks 205 and the interconnections of the logicblocks 205 can be freely altered (reconfigured) according to theconfiguration data. In other words, all the stratums including thefirst, second and third stratums are used for reconfiguration in thisexample. Note that only some of the logic blocks 205 (only the logicblocks [2, 1] and [2, 3]) are reconfigured in this example. Such apartial reconfiguration can be conducted at high speed because thenecessary volume of configuration data is small.

EXAMPLE 7

Configuration data are stored solely in a memory block 209 that isprovided in addition to the logic blocks 205 in both Example 5 andExample 6. In Example 7, configuration data are distributed among andstored in the logic blocks 205 with memory. Each of the LSI chipscomprises a memory section 210 in addition to a logic block 205 (logicsection 211) for storing configuration data that correspond to theinternal configuration of the logic block. Additionally, each of thelogic blocks can move, copy and/or replace desired configuration datafrom any of the other logic blocks by way of optical connections. Atthis time, each of the memory sections 210 always stores configurationdata that corresponds to the circuit being developed in the logic block.

Referring to FIG. 9, sequential transition of configuration data takesplace among the logic blocks [1, 1], [1, 2] and [2, 1] and, at the sametime, the configuration of the electronic circuit in each of the blockschanges. Additionally, replacement of configuration data takes placebetween the logic block [2, 3] and the logic block [3, 1] and also thatof the configuration of the electronic circuits of the logic blocks alsooccurs. Again, the number of states is not limited to two. In theinstance of FIG. 9, transitions of 2×3 or 6 states is possible.

With this technique, it is possible to realize various reconfigurationsby moving, copying and/or replacing configuration data among the logicblocks without externally loading information. Moving and copying can berealized simultaneously by multicast.

In the instance of FIG. 9, electric wires are used for the flow of dataand the flexible optical circuit is used for moving configuration data.However, inversely, the flexible optical circuit may alternatively beused for the flow of data and electric wires may alternatively be usedfor moving configuration data. In the case of replacement, the processof replacement proceeds smoothly when a vacant logic block isadditionally provided so that configuration data and the configurationof the electronic circuit are temporarily shunted there. In other words,configuration data can be moved smoothly when one of the logic blocks isdesigned to operate as buffer for configuration data.

In this example, the degree of freedom for moving, replacing and/orcopying configuration data is remarkably improved by using the flexibleoptical circuit. Particularly, configuration data can be moved, replacedand/or copied at high speed between logic blocks that are separated fromeach other by a long distance. This advantage is particularly remarkablewhen the number of logic blocks is large.

The arrangement of this example can be defined as a circuitreconfiguration technique that utilizes the third stratum. Thistechnique is characterized by an enhanced degree of freedom forreconfiguration and the capability of high-speed partialreconfiguration. It is effective for circuits that are to bereconfigured continuously on a time series basis such as real timecontrol systems.

EXAMPLE 8

In Example 8, a plurality of logic blocks 205 are reconfigured as asingle large circuit. FIG. 10 schematically illustrates areconfiguration of this example. The optoelectronic circuit of FIG. 10comprises 4×4=16 logic blocks. In this example, four ports adapted todata transmission/reception are connected to each of the logic blocks205. The degree of freedom of connection among the logic blocks 205 israised to facilitate the operation of designing a large circuitcomprising a plurality of logic blocks when a number of ports areavailable to each logic block.

A signal is input to the logic block [1, 1] and output from the logicblock [4, 4] in State A of FIG. 10. Referring to FIG. 10, the logicblocks surrounded by broken lines operate together as a large circuit inState A. The logic blocks of the large circuit are interconnected byelectric wires and/or the flexible optical circuit. In State B, a signalis input to another logic block, or the logic block [2, 1] and outputfrom the logic block [4, 4]. Here again, the logic blocks surrounded bybroken lines operate together as a large circuit. The logic blocks ofthe large circuit are interconnected by electric wires and/or theflexible optical circuit.

The function of the large circuit formed by the logic blocks surroundedby broken lines in State A and that of the large circuit formed by thelogic blocks surrounded by broken lines in State B are same andidentical. However, the two large circuits differ from each other interms of size and shape because of the difference of input section. Inother words, they differ from each other in terms of arrangement, wiringand hence circuit configuration, although they functions same.Transition from State A to State B and vice versa takes place whensignal input is switched from the logic block [1, 1] to the logic block[2, 1] and vice versa. At this time, a flag signal for circuitreconfiguration is issued and broadcast from one of the ports connectedto the logic block that operates as input section by using the flexibleoptical circuit. Then, each of the related logic blocks 205 proceeds tointernal reconfiguration using the reception of the flag signal astrigger. With this technique, transition from a state to another(reconfiguration) occurs smoothly in response to a command from thelogic block 205 to which information is input.

An enhanced degree of freedom is provided for interconnections among thelogic blocks because the optoelectronic circuit of this example also hasa flexible optical circuit. Thus, in the optoelectronic circuit, smallalteration in any of the logic blocks can lead to effective functionalalteration. Also, an enhanced degree of freedom for designing isrealized.

EXAMPLE 9

In this example again, a large circuit is reconfigured by using aplurality of logic blocks as shown in FIG. 11. However, unlike Example8, the circuit configuration surrounded by broken lines is altered andthe function is changed. The optoelectronic circuit of this examplecomprises 4×4=16 logic blocks, as shown in FIG. 11. A total of fiveports adapted to data transmission/reception are arranged at the fourcorners and at the center respectively. Each of the ports is connectedto a plurality of logic blocks 205 located in the vicinity so as to beshared by the latter. With this arrangement where a plurality of logicblocks 205 share a single port, the number of ports necessary for theoptoelectronic circuit is reduced and hence the configuration of theflexible optical circuit is simplified.

In both State A and State B of this example, the data that is processedand output is fed back to the input section as shown in FIG. 11. Theflexible optical circuit is positively used for the transmission, orfeedback, of the data. As the data passes through a plurality of logicblocks 205 as it is processed, the input section and the output sectioncan be separated from each other by a long distance. Then, the feedbackwill require a long route. Therefore, the use of the flexible opticalcircuit is preferable for the route of the feedback. At the time of thefeedback, a flag signal indicating the feedback can be broadcast to allthe logic blocks. The use of the flexible optical circuit isadvantageous for such a broadcast. Each of the related logic blocks 205reconfigures the internal circuit in response to the flag signal. Inthis example, each of the logic element in each of the logic blocks hasa memory that stores a plurality of configuration data of the logicelement. Each of the logic blocks is internally reconfigured as thefunction of the logic element is altered in response to the trigger ofthe flag signal. In this way, a reconfiguration automatically takesplace to move into the next state according to the flow of data.

With the above-described technique, the electronic circuit of each ofthe logic blocks is reconfigured in response to each feedback. In otherwords, the circuit operates as a different circuit in response to eachfeedback. Therefore, a large program can be executed by sequentiallyswitching small reconfigurable circuits.

EXAMPLE 10

The optoelectronic circuit of Example 10 is mounted with chips ofdifferent types along with a plurality of logic blocks 205. FIG. 12 is aschematic illustration of an optoelectronic circuit mounted with an ASIC(application specific integrated circuit) 212 and a memory chip 213along with a plurality of logic blocks 205. Referring to FIG. 12, thelogic blocks 205, the ASIC 212 and the memory 213 can be connectedfreely and the connections thereof can be altered (reconfigured) bymeans of the flexible optical circuit and ports.

With this arrangement, the entire circuit can be reconfigured freely byinternally reconfiguring the related logic blocks 205 and altering theinterconnections of the devices. Normally, the existence of an ASICwhose internal circuit is fixed can make any reconfiguration of theentire circuit difficult. However, the possibility of reconfiguration isremarkably improved when a flexible optical circuit is used. Since theflexible optical circuit is free from restrictions relative to thepositions of the ports in such a system, the system has a largepositional tolerance for the arrangement of the electric pins of theASIC 212 and the memory 213.

In the electrical interconnection, the positional arrangement and theconnections of the ASIC and the other additional device can be subjectedto restrictions depending on the profiles of chips, pin arrangement,etc. However, the circuit can be designed flexibly with a high degree ofredundancy when a flexible optical circuit is used. Then, the customizeddevices including the ASIC can be designed without difficulty so as toimprove their performances. In short, the optoelectronic circuit of thisexample enables customized and reconfigurable circuit showing a highdegree of redundancy and high performance.

EXAMPLE 11

The configuration of the optoelectronic circuit of this exampleresembles that of Example 1 but differs from the latter in that aprocessor array is used for the logic blocks. Each logic block compriseslogic elements, each being formed by a 32-bit arithmetic unit with anoperation frequency of 100 MHz and a 8 KB memory for holding data. Atotal of 12×12=144 logic elements are arranged. The arithmetic units areconnected by an interconnection network formed by a matrix of wires andswitches. A total of 3×3=9 logic blocks are arranged. Thus, theoptoelectronic circuit of this example is a data-flow typemulti-processor where the processors are interconnected by way of aflexible optical circuit comprising a two-dimensional optical waveguideand electric wires. It is possible to transmit instruction sets, controlsignals, interrupt signals and so on in addition to data signals bymeans of the flexible optical circuit.

The reconfigurable optoelectronic circuit of this example is adapted tohigh speed processing, using a plurality of processors for parallelprocessing. Additionally, the processor elements can be electricallyinterconnected by means of programmable switches and also by means of aflexible optical circuit. Therefore, processor elements can beinterconnected freely in a desired way to realize an efficient data flowdepending on the application of the optoelectronic circuit.

EFFECT OF THE INVENTION

As described above in detail, according to the invention, there isprovided a reconfigurable optoelectronic circuit that is large scale andoperates at high speed.

1. A reconfigurable optoelectronic circuit having an alterable internalconfiguration, comprising a plurality of logic blocks and a sheet-shapedoptical transmission medium interconnecting the logic blocks, whereineach of the logic blocks has an alterable internal configurationincluding a plurality of logic elements selectively connected viaelectric wires and switches such that the connection of the logicelements can be switched, wherein each of the logic elements has analterable internal configuration, and wherein the interconnection of thelogic blocks via the optical transmission medium is alterable.
 2. Acircuit according to claim 1, wherein configuration data of the circuitare distributed by way of said optical transmission medium and thealterable internal configuration of any of the logic blocks is alteredaccording to the configuration data.
 3. A circuit according to claim 1,wherein each of said logic blocks comprises a variable logic section anda memory section and the memory section holds configuration data thatcorresponds to the alterable internal configuration of the variablelogic section.
 4. A circuit according to claim 3, wherein said logicblock are adapted to move, copy and/or replace the alterable internalconfiguration of some other logic block by way of the opticaltransmission medium.